Vibrating aperture plates are used in a wide range of aerosol devices, and are typically supported around their rims by a vibrating support which is vibrated by a piezo element. Also, aerosol devices may have passive or static aperture plates, which operate for example by an acoustic signal from a horn causing a stream of medication to be filtered through the aperture plate.
Aerosol generators comprising a vibratable member and plate body operably coupled to the vibratable member are known. The plate body has a top surface, a bottom surface, and a plurality of apertures extending from the top surface. The apertures may be tapered such that when a liquid is supplied to one surface and the aperture plate is vibrated using the vibratable member, liquid droplets are ejected from the opposite surface. Details of such known systems are described for example in U.S. Pat. No. 6,235,177, US2007/0023547A, and U.S. Pat. No. 7,066,398, the entire contents of which are herein incorporated by reference.
Currently, aperture plates are produced by a variety of different means, including electroplating and laser drilling. Electroplating is generally the most advantageous production method from a technical and economic standpoint. U.S. Pat. No. 6,235,177 (Aerogen) describes an approach based on electroplating, in which a wafer material is built onto a mandrel by a process of electro-deposition where the liquefied metals in the plating bath (typically Palladium and Nickel) are transferred from the liquid form to the solid form on the wafer. Material is transferred to the conducting surface on the mandrel and not to the photo resist areas which are non-conducting. Areas are masked with non-conductive photo resist where metallic build-up is not required. After the conclusion of the plating process, the mandrel/wafer assembly is removed from the bath and the wafer peeled from the mandrel for subsequent processing into an aperture plate.
However, a problem with this approach is that the hole size is dependent on the plating time and the thickness of the resulting wafer. The process can be difficult to control, and if not perfectly controlled some holes may be near closed or blocked, or over-sized, and there may be out-of-tolerance variation in the sizes of the holes Also, there are limitations on the number of holes per unit of area. Further, with this technology an increase in output rate usually requires an increase in particle size, which generally may not be desired.